1. Consideration of Baffle cooling scheme
T. Sekiguchi
KEK, IPNS

2. Introduction
This document describes general considerations about cooling schemes.
Baffle = Collimator for 1st Horn
A graphite cylinder: fin = 32mm and fout = 400mm
length = 1.7m
Heat load: 4.2 kJ/pulse (1.2 kW) due to beam halo and
~1kW from back-scattered pions.
g ~2kW heat load is expected.
g Cooling is required.
For calculations, it is assumed that the heat generation is concentrated at the inner surface.
400mm
32mm
1700mm

3. Consideration of cooling scheme
Cooled by Helium or water?
Water cooling
Helium cooling
More efficient cooling
g High heat transfer coefficient
Reduce radioactive waste water
Radioactive waste water
Open circuit is not preferable
Temperature rise is very high
with low Helium flow rate
Merits
Demerits

4. Option #1 (He cooling) Helium flow
10mmf pipe
Heat load concentrates on inner part of Baffle
g Cooling inner surface is efficient.
Helium is transferred to inner cavity with 10mmf pipe.
Open circuit
Hand calculation is performed.
Helium initial temperature = 25 ºC
Very high temperature gas blows toward the beam window and the target!
g Closed circuit is preferable.
He mass flow rate (g/s) 1 2 10
(ºC)
410
218 64
Reynolds number
560
1400
9240
Heat transfer coefficient (W/m2/K)
37.9
30.1
142.5
DT between He and surface (ºC)
309
389
82.2
Tmax at graphite (ºC)
719
607
146

5. Option #2 (He cooling) Closed circuit.
He in
He out
Option #2 (He cooling)
Closed circuit.
Helium flow is divided into 6 paths.
6 holes at fhole=200mm f Not optimized.
2kW heat flow into 6 holes.
g heat flow for each hole = 333W.
Helium temperature rise is reduced since only 600W heat is cooled.
Calculation with realistic model is needed.
10mmf
200mm
(Total) He mass flow rate (g/s) 1 2 10
(ºC)
410
218 64
Reynolds number
590
1500
9650
Heat transfer coefficient (W/m2/K)
121.2
96.4
485.9
DT between He and surface (ºC)
51.5
64.7
12.8
Tmax at graphite (ºC)
466
286 80

6. Option #3 (Water cooling)
Water flow
Option #3 (Water cooling)
Cooling outer surface.
10 pipes attached on outer surface f Not optimized
2kW heat flow into 10 pipes.
g Heat flow for each pipe = 200W
Heat transfer coeff. is ~ 950W/m2/K with even 1l/min water flow.
Calculations with realistic model is needed.
To reduce the amount of radioactive waste water, the number of pipes and the pipe diameter should be reduced.
10mmf SUS
pipe
Water flow rate (l/min) 1 2 10
(ºC)
27.9
26.4
25.3
Reynolds number
2490
4970
24900
Heat transfer coefficient (W/m2/K)
950
2250
10300
DT between water and surface (ºC)
7.9
3.3
0.7
Tmax at graphite (ºC)
40.0
33.9
30.2

7. Summary Helium and water cooling are considered.
Calculations with some heat flow assumptions are performed.
In the case of He cooling, closed circuit is preferable since high temperature gas blows the beam window.
We need FEM calculations with
helium or water flows and
expected thermal load distribution.
Cooling scheme should be optimized in the cases of the options #2 and #3.

8. Supplements

9. Table #1 for calculation
Helium properties under 0.1MPa condition.
Temp (K)
Density (kg/m3)
Specific heat (kJ/kg/K)
Viscosity coeff. (mPa∙s)
Heat conductivity (mW/m/K)
Prandtlnumber
100
0.487
5.195
9.77
72.0
0.705
200
0.244
5.193
15.35
115.0
0.693
300
0.163
19.93
152.7
0.678
400
0.122
24.29
188.2
0.670
500
0.098
28.36
221.2
0.666
600
0.081
32.21
252.3
0.663
700
0.070
35.89
278.0
0.67
800
0.061
39.43
304.0
1000
0.049
46.16
354.0
0.68

10. Table #2 for calculation
Properties of water.
Temp (K)
Density (kg/m3)
Specific heat (kJ/kg/K)
Viscosty coeff. (mPa·s)
Heat conductivity (mW/m/K)
Prandtl number
273
999.8
4.217
1791.4
561.9
13.44
280
999.9
4.199
1435.4
576.0
10.46
290
998.9
4.184
1085.3
594.3
7.641
300
996.6
4.179
854.4
610.4
5.850
310
993.4
693.7
624.5
4.642
320
989.4
4.180
577.2
636.9
3.788
330
984.8
489.9
647.6
3.165
340
979.4
4.188
422.5
656.8
2.694
350
973.6
4.194
369.4
664.6
2.331

11. Simple simulations by ANSYS
Rotational symmetry model of the option #2.
Helium flow ~1g/s (0.167g/s per hole), temperature = 410 ºC
Heat conductivity around 400 ºC
~80 W/m/K (const.)
adiabatic
Heat flow at inner surface
~2kW
Heat transfer coeff.
~ 121W/m2/K
surface
~440 ºC
Hole diameter =10mm

12. Simple simulations by ANSYS
Rotational symmetry model of the option #2.
Helium flow ~1g/s (0.167g/s per hole), temperature = 410 ºC
Heat conductivity around 400 ºC
~80 W/m/K (const.)
Natural convection
~10W/m2/K
Heat flow at inner surface
~2kW
Atmospheric temp.
~60 ºC
Heat transfer coeff.
~ 121W/m2/K
surface
~360 ºC
Hole diameter =10mm

13. Simple simulations by ANSYS
Rotational symmetry model of the option #3.
Water flow ~1l/min (16.7g/s), temperature = 27.9 ºC
Heat conductivity around 30 ºC
~116 W/m/K (const.)
adiabatic
Heat flow at inner surface
~2kW
Water pipe d=10mm
Heat transfer coeff.
~ 2490 W/m2/K
inner surface
~33.7 ºC

14. Simple simulations by ANSYS
Rotational symmetry model of the option #3.
Water flow ~1l/min (16.7g/s), temperature = 27.9 ºC
Atmospheric temp
~60 ºC
Heat conductivity around 30 ºC
~116 W/m/K (const.)
Natural convection
~10W/m2/K
Heat flow at inner surface
~2kW
Water pipe d=10mm
Heat transfer coeff.
~ 2490 W/m2/K
inner surface
~34.2 ºC